The 11.2 $\mu$m emission of PAHs in astrophysical objects

TL;DR

This paper provides a theoretical model explaining the 11.2 μm emission band of PAHs in space, linking spectral variations to PAH size and charge states using DFT calculations and astrophysical data.

Contribution

It introduces a detailed emission model based on DFT calculations that accounts for PAH size, temperature, and charge effects to interpret astronomical spectra.

Findings

The 11.2 μm band asymmetry is mainly due to PAH mass distribution.

Profile variations are explained by differences in PAH size and charge.

The model successfully reproduces observed spectral features.

Abstract

The 11.2 $\mu$m emission band belongs to the family of the `Unidentified' Infrared (UIR) emission bands seen in many astronomical environments. In this work we present a theoretical interpretation of the band characteristics and profile variation for a number of astrophysical sources in which the carriers are subject to a range of physical conditions. The results of Density Functional Theory (DFT) calculations for the solo out-of-plane (OOP) vibrational bending modes of large polycyclic aromatic hydrocarbon (PAH) molecules are used as input for a detailed emission model which includes the temperature and mass dependence of PAH band wavelength, and a PAH mass distribution that varies with object. Comparison of the model with astronomical spectra indicates that the 11.2 $\mu$m band asymmetry and profile variation can be explained principally in terms of the mass distribution of neutral PAHs with a small contribution from anharmonic effects.